Caption: 5d electron orbitals, computer model. An electron orbital is a region around an atomic nucleus (not seen) in which one or a pair of electrons is most likely to exist. Four of the five 5d orbitals are made up of four tri-lobed lobes, centred on the nucleus. The orbital at top right comprises two tri-lobed lobes with a concentric pair of equatorial rings. The 5 shell also contains one spherical 5s orbital and three lobed 5p orbitals, both at a lower energy, and seven lobed 5f orbitals at a higher energy level (not seen). The 5d shells are partially full in the third row of transition metals, which typically form coloured compounds as electron transitions between 5d orbitals absorb some visible wavelengths of light.